1. Field of the Invention
The present invention relates to an apparatus that is attached to an engine under test and detects the compression top dead center during the compression stroke of that engine.
2. Description of the Related Art
Conventionally, apparatuses for so-called “cold testing” have been used to test an engine without running it. This type of apparatus is provided with a driving portion that is connected to the engine's crankshaft and that forces that crankshaft to rotate to perform various kinds of engine tests, such as for the open and close timing of the intake valve or the exhaust valve.
Such cold testing is performed not only on finished engines, but also on engines that are not fully assembled, such as engines to which the injection nozzles and spark plugs have not yet been installed. Such engine testing can, thus, reduce the manpower necessary for any design changes.
When performing the various engine tests mentioned above, the compression top dead center of the engine being tested is ordinarily set as a reference point. Here, the compression top dead center is defined as the phase of the crankshaft corresponding to the top dead center of the piston during a compression stroke of the engine under test. Consequently, the compression top dead center of the engine under test needs to be detected before the engine tests.
Among conventional compression top dead center detection apparatuses, as disclosed for example in JP 2001-82238A, there are apparatuses that detect the compression pressure within the cylinders with pressure sensors that are attached to mounting holes for the injection nozzles or spark plugs of the engine under test. These apparatuses rotate the crankshaft of the engine under test from the outside with a motor, detect the rotation phase of the crankshaft with a rotation sensor, furthermore detect the phase of the crankshaft corresponding to the maximum pressure detected by the pressure sensor, and detect the compression top dead center phase from the phase corresponding to this maximum pressure point, thus detecting the compression top dead center while the injection nozzles and spark plugs have not yet been installed.
In the above-mentioned JP 2001-82238A, the crankshaft is rotated at various rotation speeds from slow speeds to high speeds, and the maximum pressure phase is determined for each of those rotation speeds. Based on the relation between these maximum pressures phases and the rotation speeds, an experimental function is determined that has an asymptotic line for infinitely large rotation speeds, and the phase corresponding to this asymptotic line is detected as the compression top dead center phase.
However, there are times when engine testing has to be performed with the injection nozzles and spark plugs already put in place. But with the above-described conventional apparatus, this is not possible, because it is designed to use the mounting holes for the injection nozzles and spark plugs of the engine to mount the pressure sensors.